"Damage" to subspace I envision as ripping voids in the fabric of subspace. I have treknobabblized that subspace is the dimension of gravity consisting of a medium of gravitons that congruently overlies our real universe. The mass of an object draws gravity from this dimension causing gravity in the real universe. At the same time, masses create gravity wells and many variable disturbances in the subspace gravity medium.
The energy to poke a photon (a no mass radio wave) into subspace is enormous (or easy with transtator technology

), and poking anything with mass into this dimension is nigh impossible. Subspace radio is actually radio waves traveling in this medium but the radio wave travels at infinite speed (it has no other dimension) but the strength of the signal still falls off by the inverse square law from its initiation point in the real universe to another point someplace else in the real universe. As a result, detection of weak signals after a few light years equivalent distance in the real universe is hard to detect due to the noisy subspace background radio clutter. To pass a strong enough radio signal vast distances, it requires subspace radio boosters/relays. As for subspace damage such as zones of nothing or "voids", radio waves are absorbed into the blackness and not transmitted nor reflected past a void.
Certain sensors operate just like radar but in subspace. Subspace radio waves bounce off gravity wells (i.e. masses) an other disturbances, then echo back instantly. The sensor can measure the mass of the object, and if it is moving, the course and speed info. Suns and planets are big easy targets to sense from many light years, but smaller masses can also be detected but at closer ranges since their reflection is much smaller thus a weaker return signal. This gives info to a ship as to mass obstacles in its path or other ships in your detection vicinity. (I think this is the deflector's sensor used in
Balance of Terror to detect and crudely target the cloaked Romulan ship.) Voids would black out these sensors.
I have more ideas involving impulse engines translating gravity out of subspace for reaction-less propulsion (large linear transtators powered by warp power or fusion reactors), series of really large coil transtators powered by M/AM reactors used condense space-time (space warp) around the ship, and all sorts of gravity and antigravity devices, but diner is up and I'm going to go eat.